This invention relates to an electrostatographic reproducing apparatus and more particularly to a novel corona generating device together with an end block assembly designed to minimize the occurrence of hazardous or unsafe conditions.
In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member is typically charged to a positive potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the support surface the photoconductive insulating surface may be discharged and cleaned of residual toner to prepare for the next imaging cycle.
In such electrostatographic apparatus in use today, corona generating devices are used for several purposes; to initially uniformly charge the electrostatographic imaging member, to electrostatically transfer the toner particles from the imaging member to a receiving surface such as ordinary paper, to detack the transfer member (copy paper) from the imaging member. In certain machine configurations, corona generating devices may also be used as pre-charge corotrons, pre-transfer corotrons, and preclean corotrons.
Typically these charging devices comprise a corona discharge wire made of tungsten, stainless steel, or platinum of about 0.5 mm to 0.15 mm, preferably 0.1 mm in diameter spaced in opposed relation with the surface of the photosensitive member. A high voltage is applied across the wire thereby producing the corona discharge, which imparts the electrostatic charge to the surface of the photosensitive member.
Since a high voltage is applied, the corona discharge wire is gradually corroded and deteriorated so that the tensile strength of the wire may be so reduced as to cause the breakage. Furthermore, when the toner or the like is attached to the corona discharge wire, the corona discharge tends to be concentrated at one portion so that a spark discharge may be produced thereby causing the breakage of the wire. In some cases, the copying paper is wrapped around the charging device and brought into contact with the corona discharge wire, thus resulting in the breakage. When a fractured live wire is present, arcing and sparking may rapidly occur and the electrophotographic apparatus itself may be damaged and an operator may suffer electric burns or shock by contacting the wire.
Furthermore, when the live fractured wire contacts the photosensitive member, it may damage the photosensitive member in effect burning off the photosensitive coating on the member which depending on the materials that it contains, may result in the evolution of toxic or noxious fumes. Accordingly, when a high voltage coronode wire does rupture, a cause for customer concern and safety are presented.
While, as discussed above, the wire may be fractured as a result of gradual corrosion or deterioration it should be noted that a number of external factors may also contribute to fracture of a coronode wire, including such diverse things as machine vibration, chance contact by any conductive member upon which the coronode wire tends to melt including contact by a plurality of conductive fibers in the surrounding air.